The effect of Tb407 on electrical behavior of the ZnO-Pr6Oll-based varistor ceramics was investigated. Microstructural analysis indicated that the addition of Tb407 decreased average grain size from 3.6 to 3.2 and inc...The effect of Tb407 on electrical behavior of the ZnO-Pr6Oll-based varistor ceramics was investigated. Microstructural analysis indicated that the addition of Tb407 decreased average grain size from 3.6 to 3.2 and increased the sintered density from 5.58 to 5.68 g/cm3. As the amount ofTb407 increased, the breakdown field increased from 9393 to 12437 V/cm and the nonlinear coefficient increased from 50 to 65. The varistor ceramics added with 0.5 mol.% in the amount of Tb407 exhibited an excellent stability by exhibiting 0. 1% in the variation rate of the breakdown field, 0% in the variation rate of the nonlinear coefficient, and 8.8% in the variation rate of the leakage current density for DC-accelerated aging stress of 0.85 E1 mA/115 ℃/24 h.展开更多
In contrast to conventional transformers, power electronic transformers, as an integral component of new energy power system, are often subjected to high-frequency and transient electrical stresses, leading to heighte...In contrast to conventional transformers, power electronic transformers, as an integral component of new energy power system, are often subjected to high-frequency and transient electrical stresses, leading to heightened concerns regarding insulation failures. Meanwhile, the underlying mechanism behind discharge breakdown failure and nanofiller enhancement under high-frequency electrical stress remains unclear. An electric-thermal coupled discharge breakdown phase field model was constructed to study the evolution of the breakdown path in polyimide nanocomposite insulation subjected to high-frequency stress. The investigation focused on analyzing the effect of various factors, including frequency, temperature, and nanofiller shape, on the breakdown path of Polyimide(PI) composites. Additionally, it elucidated the enhancement mechanism of nano-modified composite insulation at the mesoscopic scale. The results indicated that with increasing frequency and temperature, the discharge breakdown path demonstrates accelerated development, accompanied by a gradual dominance of Joule heat energy. This enhancement is attributed to the dispersed electric field distribution and the hindering effect of the nanosheets. The research findings offer a theoretical foundation and methodological framework to inform the optimal design and performance management of new insulating materials utilized in high-frequency power equipment.展开更多
Long-term research has been done on the unstable behaviors and electron emission from microprotrusions, but the whole reason is still not clear. It is difficult to study instabilities experimentally since vacuum break...Long-term research has been done on the unstable behaviors and electron emission from microprotrusions, but the whole reason is still not clear. It is difficult to study instabilities experimentally since vacuum breakdown can happen. In this model, we show the factors that lead to thermal instability during field emission. After the Nottingham flux inversion, we see a considerable rise in temperature above a threshold electric field, followed by a thermal runaway. Cathode spots experience unexpected thermal defects and breakdowns, which is a phenomenon known as the Nottingham Inversion Instability. Although the idea of micro protrusions is frequently used in modeling studies, this study concentrates on the thermal effects during field emission from a planar cathode without taking the existence of such protrusions into account. The study reveals how Nottingham’s heating effect changes from heating to cooling. In our study, we have investigated the interaction between Nottingham, Joule heating, and effective work function. The results also imply that faster reaching critical temperature is associated with larger maximum beta values. These discoveries have significance for the design and improvement of high-voltage systems and help to understand vacuum breakdown. The possibility of cathode spot ignition and subsequent vacuum breakdown is predicted by our model, which would make it possible to create a self-consistent model for that.展开更多
文摘The effect of Tb407 on electrical behavior of the ZnO-Pr6Oll-based varistor ceramics was investigated. Microstructural analysis indicated that the addition of Tb407 decreased average grain size from 3.6 to 3.2 and increased the sintered density from 5.58 to 5.68 g/cm3. As the amount ofTb407 increased, the breakdown field increased from 9393 to 12437 V/cm and the nonlinear coefficient increased from 50 to 65. The varistor ceramics added with 0.5 mol.% in the amount of Tb407 exhibited an excellent stability by exhibiting 0. 1% in the variation rate of the breakdown field, 0% in the variation rate of the nonlinear coefficient, and 8.8% in the variation rate of the leakage current density for DC-accelerated aging stress of 0.85 E1 mA/115 ℃/24 h.
基金supported in part by the National Key R&D Program of China (No.2021YFB2601404)Beijing Natural Science Foundation (No.3232053)National Natural Science Foundation of China (Nos.51929701 and 52127812)。
文摘In contrast to conventional transformers, power electronic transformers, as an integral component of new energy power system, are often subjected to high-frequency and transient electrical stresses, leading to heightened concerns regarding insulation failures. Meanwhile, the underlying mechanism behind discharge breakdown failure and nanofiller enhancement under high-frequency electrical stress remains unclear. An electric-thermal coupled discharge breakdown phase field model was constructed to study the evolution of the breakdown path in polyimide nanocomposite insulation subjected to high-frequency stress. The investigation focused on analyzing the effect of various factors, including frequency, temperature, and nanofiller shape, on the breakdown path of Polyimide(PI) composites. Additionally, it elucidated the enhancement mechanism of nano-modified composite insulation at the mesoscopic scale. The results indicated that with increasing frequency and temperature, the discharge breakdown path demonstrates accelerated development, accompanied by a gradual dominance of Joule heat energy. This enhancement is attributed to the dispersed electric field distribution and the hindering effect of the nanosheets. The research findings offer a theoretical foundation and methodological framework to inform the optimal design and performance management of new insulating materials utilized in high-frequency power equipment.
文摘Long-term research has been done on the unstable behaviors and electron emission from microprotrusions, but the whole reason is still not clear. It is difficult to study instabilities experimentally since vacuum breakdown can happen. In this model, we show the factors that lead to thermal instability during field emission. After the Nottingham flux inversion, we see a considerable rise in temperature above a threshold electric field, followed by a thermal runaway. Cathode spots experience unexpected thermal defects and breakdowns, which is a phenomenon known as the Nottingham Inversion Instability. Although the idea of micro protrusions is frequently used in modeling studies, this study concentrates on the thermal effects during field emission from a planar cathode without taking the existence of such protrusions into account. The study reveals how Nottingham’s heating effect changes from heating to cooling. In our study, we have investigated the interaction between Nottingham, Joule heating, and effective work function. The results also imply that faster reaching critical temperature is associated with larger maximum beta values. These discoveries have significance for the design and improvement of high-voltage systems and help to understand vacuum breakdown. The possibility of cathode spot ignition and subsequent vacuum breakdown is predicted by our model, which would make it possible to create a self-consistent model for that.
